The root canals were then instrumented using the crown-down
technique and rotary instruments (ProTaper, Dentsply Maillefer,Ballaigues, Switzerland), and the canals were enlarged to an apical
size F3. Two milliliters of 3% NaOCl was used between each instrument
during the cleaning and shaping procedure. All the teeth were then vertically
sectioned along the midsagittal plane into two halves. The concave
tooth surface was minimally grounded to achieve a flat surface to enable
placement in the tissue culture wells, exposing the root canal surface to
E. faecalis to form a biofilm.